Making sense of the Jegan's evolution

[False Prophet]

So, I understand the various development lineages of the Jegan as follow (I'm not talking about CCA-MSV):

1. Jegan => Jegan Ground Type/Jegan Type-A2 => Jegan Type J/M/R => Heavygun

2. Jegan => Jegan Type D => Jegan (ECOAS)/Escort Type/EWAC

3. Jegan => Prototype Stark Jegan => Stark Jegan

(The Prototype Stark Jegan was based on the original Jegan, while the Stark Jegan was just a modified Jegan Type D.)

My question is that whether the Jegan Type D was developed after or in parallel to the Type-A2? Also, could you think of a good in-universe reason why did the EFF abandon the Jegan Type D and its variants to continue developing the Jegan Type-A2?

P/S: I am surprised that Sunrise hasn't made a sniper Jegan.

[yazi88]

Type D is a minor update of the original Jegan.

Most things are either developed from the original Jegan and the Type D. Jegan's multi-role design allows are various upgrades/variations. It really does have quite a number of them.

[Kuruni]

3. Jegan => Prototype Stark Jegan => Stark Jegan

More like this (as far as I understand). They develope Prototype Stark Jegan from normal Jegan, then made the Jegan Type D from Jegan so it would be easier to modify it into Stark Jegan.

[Mafty]

How exactly does the Jesta tie in to all of this?

[Seto Kaiba]

How exactly does the Jesta tie in to all of this?

The Jesta's a high-spec derivative of the Jegan made to operate in support of the RX-0.